Re: [Xen-devel] Question about MDS mitigation

["wencongyang (A)" <wencongyang2@xxxxxxxxxx>]

On 2019/5/16 15:58, Andrew Cooper wrote:
> On 16/05/2019 08:56, wencongyang (A) wrote:
>>
>> On 2019/5/16 15:38, Andrew Cooper wrote:
>>> On 16/05/2019 03:46, wencongyang (A) wrote:
>>>> Hi all
>>>>
>>>> Fill buffers, load ports are shared between threads on the same physical 
>>>> core.
>>>> We need to run more than one vm on the same physical core.
>>>> Is there any complete mitigation for environments utilizing SMT?
>>> No - not really.
>>>
>>> An approach which was worked on was that of synchronised scheduling,
>>> whereby privilege transitions are syncrhonised to ensure that we're
>>> never running code from different privilege levels concurrently on
>>> adjacent threads.  (This is the mitigation described as Group Scheduling
>>> in
>>> https://software.intel.com/security-software-guidance/insights/deep-dive-intel-analysis-microarchitectural-data-sampling
>>> )
>> synchronised scheduling is not a complete mitigation. Guest A and Guest B
>> run on the same physical core, and the privilege level is the same. So
>> Guest A can infer data from Guest B. Guest A cannot infer data from 
>> hypervisor
>> because they are in different privilege levels.
> 
> This is (one of the reasons) why core scheduling is a prerequisite to
> synchronised scheduling.
> 
> With core scheduling active, you will never have guest A and B
> concurrently running on adjacent threads of the same core.

Thanks for you explanation. I got it.

Wen Congyang

> 
> ~Andrew
> 
> 


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